G'day and welcome.
What you're trying discipline-wise is fairly typical of parents of 'normal' kids, but it is punishment-based. We know a lot more about what works best with kids, and positive reinforcement works better by a mile. We tend as parents to begin to view this as a competition between us and the kids, and that is when our problems can really begin to ramp up.
I don't know your child, but I can hazard a guess; he struggles and needs certain strategies to help him manage. He will be developing his own strategies (which are not always as good as ones we could give them, but what our kids do for themselves sticks stronger) and he will be wanting to do things his own way.
For example - my boys use computer gaming to help them calm down. Having a lot of homework pushes anxiety up, so to calm down, the boys get onto the computer games (instead of doing the homework). This means that the stress level increases (teachers demanding homework get handed in) so it gets worse and worse going round and round. Sometimes the games are a genuine help, but within reason and in moderation. You can't always reason with a kid, you have to lead them and not push. You also need consistency.
A good way to begin - observe your child. Identify what triggers him, also what soothes him. Use this information. Ease off the stress for a while, call off the dogs (ie ask the school to can the homework for a while if you can, especially if it's a huge trigger). Teach your child that you are a support, not an obstacle. Engage the child and cut way back on what you're going to get upset about. Don't try to fix all the problems at once because it is just too overwhelming for a child to hear, "Sit up! Elbows off the table! Don't talk with your mouth full! Don't roll your eyes! Don't answer back! Speak up! Don't swear!" and so on, over and over. It just won't sink in.
Instead, catch him out doing something good and praise him for it. "I really like the way you helped your friend when he hurt himself. That was very kind of you to do that."
Read the books (Explosive Child etc). They do help a lot. Really. Get them out of your local library if you're wary of buying new books; by now, most of us have full shelves and want to read a book first to make sure it will help.
So don't take my word for it. Read it. And hopefully once you can begin to make some changes, you will find it makes your workload easier.
Marg